curred. Thus, the identification of such chi struc- tures provides evidence for cross-over events taking place between circular DNA molecules. chitin a polymer of high molecular weight com- posed of N-acetylglucosamine residues joined to- gether by beta glycosidic linkages between carbon atoms 1 and 4. Chitin is a component of the exoskel- etons of arthropods. chlamydia obligate intracellular parasites or sym- bionts found throughout the animal kingdom.
Some chlamydia have existed as endosymbionts of free-liv- ing amoebae since Precambrian times. The most common sexually transmitted disease in the U.S. is caused by Chlamydia trachomatis. Its genome con- sists of a 1,042,519 base pair chromosome and a 7,493 bp plasmid.
See Appendix A, Prokaryotes, Bac- teria, Pirellulae; Appendix C, 1998, Stephens et al.; Appendix F. Chlamydomonas reinhardi a species of green al- gae in which the interaction of nuclear and cyto- plasmic genes has been extensively studied. The nu- clear gene loci have been distributed among 17 linkage groups.
Nuclear genes are transmitted to the offspring in a Mendelian fashion, but chloroplast and mitochondrial DNAs are transmitted uniparentally. The mating-type “+” parents transmit chloroplasts, while the “−” parents transmit mitochondria.
The chloroplast DNA contains nearly the same set of genes that encode rRNAs, tRNAs, ribosomal pro- teins and photosynthetic proteins as are found in the chloroplast DNAs of higher plants. The genetic anal- ysis of the flagellar apparatus of Chlamydomonas has identified more than 80 different mutations that af- fect its assembly and function. The axoneme con- tains more than 200 proteins, most of which are unique to this structure. An alternative spelling, C. reinhardtii, occurs in the literature. See Appendix A, Protoctista, Chlorophyta; Appendix C, 1963, Sager and Ishida; 1970, Sager and Ramis; Appendix E. chlorambucil a drug that binds DNA strands so that the double helix cannot unzip and replicate. Therefore it suppresses cell division and is used in cancer chemotherapy.
See alkylating agent. chloramphenicol an antibiotic produced by Strep- tomyces venezuelae. Chloramphenicol is a potent in- hibitor of protein synthesis on the 70S ribosomes of prokaryotes. It attaches to the 50S ribosomal sub- unit and prevents the addition of an amino acid to the growing polypeptide chain. Chloroamphenicol does not bind to the 80S ribosomes of eukaryotes, but it does bind to the smaller ribosomes of the mi- tochondria present in eukaryotic cells. This is one of